Generally, a display device is provided with wide viewing angle such that more users can see the images displayed by the display device. However, under some circumstances, such as when reading confidential data or when inputting password, the wide viewing angle display effect makes it possible for other people around the display device to see the confidential data, which increases the risk of data leak. Therefore, to fulfill the two different requirements of providing images for more users at the same time and reading confidential data in public place wherever necessary, a display device that can be switched between a wide viewing angle mode and a narrow viewing angle mode has been expected as a mainstream product in display device market.
The conventional anti-peeping mechanisms for display device can be mainly classified as the following approaches:
1. Adding Additional Anti-Peeping Film to the Surface of Substrate of the Display Device:
The anti-peeping film can restrain the brightness of wider viewing angle, and thus people aside the display device cannot clearly read the displayed image. The anti-peeping film is a commonly-used material, though; the additional anti-peeping film will adversely affects the optical property and display quality of the display device when displaying images for the user in front of the display device. Also, the user has to manually switch the anti-peeping film, which causes inconvenience.
2. Backlight Source Control:
The switching between wide viewing mode and narrow viewing mode can be achieved by using a backlight source with high collimation accompanied with a diffusion sheet able to be controlled by voltage e.g. a polymer dispersion liquid crystal (PDLC) film. For example, when no voltage is applied, the diffusion sheet will diffuse the collimated backlight, so that the backlight can emit in the side viewing direction. Thus, the wide viewing mode can be provided. When a voltage is applied, the diffusion sheet will not diffuse the collimated backlight. Thus, the narrow viewing mode can be provided. To be exact, this approach adjust the brightness of the backlight emitting in the side viewing direction by controlling the emitting angle of the backlight, so that people cannot see the display image in the side viewing direction. In practical application, it is difficult to control the light route, and thus a perfect collimated backlight cannot be obtained. In such a case, the brightness of the backlight emitting in the side viewing direction may be reduced to a certain extent, but the brightness of the backlight emitting in the side viewing direction is yet not ignorable. As a result, the anti-peeping effect is not satisfactory.
3. Adding a Viewing Angle Control Module:
The switching between wide viewing mode and narrow viewing mode can be achieved by adding an additional viewing angle control module to the display device (panel). In the wide viewing mode, the viewing angle control module does not cause any interference or damage on the displayed image; in the narrow viewing mode, the viewing angle control module can restrain the brightness in the side viewing direction, such that people cannot clearly read the display image in the side viewing direction. However, this approach requires two modules including the display module and the additional viewing angle control module, and thus the overall weight and thickness is doubled. Also, the cost is highly increased.
It can be seen that the aforementioned conventional anti-peeping approaches have to sacrifice some of the original characteristics such as display quality, optical property, thickness and weight for providing the anti-peeping effect, and thus need to be improved.